1. Field of the Invention
This invention relates to improved delivery devices and methods for delivering transcatheter prosthetic valves, and particularly to device and methods for delivering expandable prosthetic heart valves.
2. Background of the Invention
Cardiac interventionalists are now able to perform complex surgical procedures without the need for a full surgical team and operating room staff thanks to endoscopic methods and devices developed over the last few decades. Cardiac surgeons have now become in some instances technicians relied upon only when the traditional cutting and sewing techniques are necessary. Cardiac catheterization labs and outpatient procedures are now commonplace and patients are familiar with the concept that tools, cameras, stents, valves, and other items may be inserted via endoscopic methods into a patient for treatment or diagnosis.
There are many ways of endoscopically accessing a heart for treatment. Using a modified Seldinger technique of using a sheathed puncturing device to access an artery and leaving the sheath in place as a lumen down which catheters and other interventional tools may be deployed, cardiac interventionalists have been able to access the heart in an off-pump manner. Traditional procedures involve accessing via the femoral artery, but also known are procedures for accessing the heart in a retrograde manner through the aortic arch or in an antegrade manner through the right atrium and making a transeptal cut. These techniques have been used successfully for the deployment of various stents, valves, and various surgical appliances such as annular rings and so forth, as well for delivery of radiologic agents and medicines. It is worth noting that none of these procedures are particularly easy to perform and there are striking differences between the various uses. For instance, using a balloon to expand a coated metal stent scaffold in a clogged coronary artery, is very different from using multiple catheter tools to deliver and stitch a new prosthetic valve into the interior of a diseased heart. There are differences in planning, imaging e.g. echocardiography, differences in tools, length of procedure, risk of complication, types of patients, pathologies that are treatable, and so forth.
Prosthetic heart valves pose particular challenges for delivery and deployment. Valvular heart disease and specifically aortic and mitral valve disease is a significant health issue in the US. Annually approximately 90,000 valve replacements are conducted in the US. Traditional valve replacement surgery, the orthotopic replacement of a heart valve, is an “open heart” surgical procedure. Briefly, the procedure necessitates surgical opening of the thorax, the initiation of extra-corporeal circulation with a heart-lung machine, stopping and opening the heart, excision and replacement of the diseased valve, and re-starting of the heart. While valve replacement surgery typically carries a 1-4% mortality risk in otherwise healthy persons, a significantly higher morbidity is associated to the procedure largely due to the necessity for extra-corporeal circulation. Further, open heart surgery is often poorly tolerated in elderly patients.
Thus if the extra-corporeal component of the procedure could be eliminated, morbidities and cost of valve replacement therapies would be significantly reduced.
While replacement of the aortic valve in a transcatheter manner is the subject of intense investigation, lesser attention has been focused on the mitral valve. This is in part reflective of the greater level of complexity associated to the native mitral valve apparatus and thus a greater level of difficulty with regards to inserting and anchoring the replacement prosthesis.
Several designs for catheter-deployed (transcatheter) aortic valve replacement are under various stages of development. The Edwards SAPIEN transcatheter heart valve is currently undergoing clinical trial in patients with calcific aortic valve disease who are considered high-risk for conventional open-heart valve surgery. This valve is deployable via a retrograde transarterial (transfemoral) approach or an antegrade transapical (transventricular) approach. A key aspect of the Edwards SAPIEN and other transcatheter aortic valve replacement designs is their dependence on lateral fixation (e.g. tines) that engages the valve tissues as the primary anchoring mechanism. Such a design basically relies on circumferential friction around the valve housing or stent to prevent dislodgement during the cardiac cycle. This anchoring mechanism is facilitated by, and may somewhat depend on, a calcified aortic valve annulus. This design also requires that the valve housing or stent have a certain degree of rigidity.
At least one transcatheter mitral valve design is currently in development. The Endovalve uses a folding tripod-like design that delivers a tri-leaflet bioprosthetic valve. It is designed to be deployed from a minimally invasive transatrial approach, and could eventually be adapted to a transvenous atrial septotomy delivery. This design uses “proprietary gripping features” designed to engage the valve annulus and leaflets tissues. Thus the anchoring mechanism of this device is essentially equivalent to that used by transcatheter aortic valve replacement designs.
Accordingly, there still remains a need for improved delivery devices and methods for transcatheter mitral valve replacements.